Optical communication technology which uses optical carrier waves to transport data is now being developed, and in recent years, optical waveguides are becoming increasingly widespread as a means of guiding these optical carrier waves from one point to another. These optical waveguides have a linear core portion and a cladding portion provided so as to cover the periphery of the core portion. The core portion is composed of a material that is essentially transparent to the light of the optical carrier waves, and the cladding portion is composed of a material having a lower refractive index than that of the core portion.
In an optical waveguide, light introduced from one end of the core portion is transported to the other end while reflecting off the boundaries with the cladding portion. A light emitting element such as a semiconductor laser is disposed at the input side of the optical waveguide, and a light receiving element such as a photodiode is disposed at the output side. The light input from the light emitting element is transmitted through the optical waveguide and is received by the light receiving element, and communication is conducted on the basis of a blinking pattern or intensity pattern of the received light.
The use of these types of optical waveguides in supercomputers and large-scale servers and the like is being investigated. Conventional supercomputers are constructed by installing a plurality of electrical circuit boards mounted with semiconductor elements and electronic components and the like in racks, and then electrically connecting these electrical circuit boards to one another. Investigations are being conducted for such structures, for example, into substituting electrical connections within individual electrical circuit boards, electrical connections between electrical circuit boards and electrical connections between racks with optical connections using optical fibers. It is anticipated that these substitutions will enable greater volumes of information transmission, increased speed, and reduced energy consumption and the like, resulting in improved supercomputer performance.
In order to achieve these optical connections, optical fiber sheets are being investigated in which a plurality of optical fibers are bundled together in an intersecting state, with connectors provided at the ends of the fibers (for example, see Patent Document 1).
In order to replace electrical wiring with this type of optical fiber sheet, light receiving and emitting elements and connectors are installed on the electrical circuit board. Then, by linking the electrical circuit board side connectors with the optical fiber ribbon side connectors, optical connections are achieved. Further, devices in which light receiving and emitting elements are installed on the side of the optical fiber sheet are also being investigated.
However, these optical fiber sheets are formed by sandwiching the intersecting portions of the optical fibers between film substrates. Accordingly, the optical fibers overlap at the optical fiber intersecting portions, meaning an increase in the sheet thickness at these portions is unavoidable. Consequently, the sheets are difficult to bend during optical connection operations, and there is a possibility that the optical fibers may break when bent with excessive strength. As a result, there are various restrictions associated with the wiring space and the wiring operations.
Further, in consideration of resistance to transverse rupture and the like, making the optical fibers finer is problematic. Accordingly, the spacing between the core portions of adjacent optical fibers cannot be narrowed more than conventional structures, meaning there is a limit to possible improvements in the wiring density.